IONIC EFFECTS ON GLUCOSE TRANSPORT AND METABOLISM BY ISOLATED MOUSE FAT CELLS INCUBATED WITH OR WITHOUT INSULIN .3. EFFECTS OF REPLACEMENT OF NA+

1. 1. The replacement of Na+ in the medium leads to the alterations in glucose metabolism by isolated mouse fat cells. In the absence of insulin, replacement of Na+ by other cations leads to increased uptake and metabolism of glucose at all concentrations of glucose tested. 2. 2. In the presence of insulin, replacement of Na+ strikingly decreases glucose uptake and metabolism, thereby suggesting that insulin-stimulated glucose transport into fat cells is dependent on Na+. Glucose uptake is not, however, directly proportional to the concentration of Na+ in the incubation medium. 3. 3. The decreased insulin-stimulated glucose uptake and metabolism resulting from Na+ replacement in the medium is not due to irreversible structural damage, since insulin-stimulated cells preincubated in Na+-free medium may regain near-normal ability to transport and metabolize glucose when transferred to medium of normal Na+ concentration. 4. 4. In the presence of normal Na+ concentrations, the maximal velocity of glucose uptake and metabolism by insulin-stimulated fat cells is increased, while the apparent overall Km of glucose uptake is unchanged. 5. 5. It is postulated that insulin activates a carrier which binds and transports Na+ along with glucose molecules. It is recognized that this concept must remain hypothetical for the time being. © 1969.